What Are Blockchain and Distributed Ledger Technology ("DLT")?

We've all heard of the blockchain technology allegedly 'disrupting' all kinds of industries. Blockchain had promised to introduce a key 'digital' element in disparate fields, from finance to tech, and even to that conservative beast called 'the Law' - but so far such promises have not borne fruit. The question is, what is blockchain? Essentially, it can be considered as a form of Distributed Ledger Technology ("DLT").